Method and apparatus for manufacturing positive electrode foil of aluminum electrolytic capacitor

ABSTRACT

A method of manufacturing a positive electrode foil of an aluminum electrolytic capacitor is provided in which anodizing conditions are optimally determined and automatically set to minimize the loss of production and to produce a constant quality of the positive electrode foil. The method comprises an etching process and an anodizing process. An etched foil produced in the etching process is subjected to a constant current inspection, and then, the anodizing conditions are determined from the result of the constant current inspection. The anodizing conditions are transferred to a control panel in the anodizing process where they are automatically registered as its settings. Also, an apparatus for manufacturing the positive electrode foil is provided which has a voltage sensor connected between an output running roller and cathode electrodes in an anodizing tank. A voltage measured by the voltage sensor is fed back to a direct-current source for controlling its output voltage.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for manufacturing a positive electrode foil of an aluminum electrolytic capacitor.

BACKGROUND OF THE INVENTION

Aluminum electrolytic capacitors are widely used in the circuits of electronic apparatuses. A common type of aluminum electrolytic capacitor comprises a capacitor element having a positive electrode foil and a negative electrode foil separated by a separator and wound to a roll, a driving liquid electrolyte permeated into the capacitor element, and a metal case accommodating the capacitor element.

The positive electrode foil is conventionally manufactured by the following procedure. An aluminum foil is etched to increase its effective surface area and coated by anodizing process with a dielectric oxide film. The effective surface area is controlled with determining the etching conditions, Controlling an applied voltage in an anodizing process determines a thickness of the film, and thereby, a rated voltage and a capacitance of a finished capacitor can be controlled.

FIG. 7 is a flowchart of a conventional procedure of manufacturing the positive electrode foil. In the etching process, an aluminum foil 71 having a thickness of 0.05 to 0.11 mm and a length of about 5000 m provided in a coil form is continuously etched by the etching operation 72 in an etching apparatus. The apparatus is equipped with a control panel 73 manually preset with the etching conditions for a desired effective surface area. The etched foil 74 is rolled in every 1,000 m into a coil specified with a lot number. Each lot of the etched foil 74 is then subjected to a characteristic inspection 75 (conforming to EIAJ RC-2364A).

In general, a number of the etching apparatuses are used for manufacturing the etched foils 74 having the same effective surface area.

In the anodizing process, each etched foil 76 is continuously impressed with a constant voltage in the anodizing operation 77 in an anodizing apparatus to obtain a dielectric oxide film, i.e., an anodized foil 79. The anodizing apparatus is equipped with a control panel 78 preset manually with the anodizing conditions based on the rated voltage and the desired effective surface area of the etched foil 74. The anodizing conditions may include predetermined levels (data from the preceding experiments and production) of applied voltage and current and temperatures in the anodizing process.

The anodized foil 79 is then subjected to a characteristic inspection 80 (conforming to EIAJ RC-2364A) and a judgment 81 before a finished positive electrode foil 82 is released.

If, in the characteristic inspection 80, it is judged that the resultant rated voltage and capacitance are not desired values, the anodizing conditions are updated to obtain them.

FIG. 8 illustrates such an anodizing apparatus. The anodizing apparatus is fed with an etched foil 91 generally having a thickness of 0.05 to 0.11 mm, a width of 500 mm, and a length of 500 to 1,000 m. The etched foil 91 is passed over a feed roller 92 connected to the positive electrode of a first direct-current source 97 and introduced by a running roller 93 into an anodizing tank 96. The anodizing tank 96 has a plurality of cathode electrodes 95 arranged therein in parallel with the etched foil 91 to be passed and is filled with an anodizing processing liquid. In the anodizing tank 96, the etched foil 91 serving as the positive electrode is anodized to obtain a dielectric oxide film thereon. The etched foil 91 coated with the dielectric oxide film is pulled out from the anodizing tank 96, and then, conveyed via a depolarization tank 98 to a first re-anodizing tank 99 and a second re-anodizing tank 101. Each of the re-anodizing tanks 99 and 101 has a plurality of cathode electrodes arranged therein and connected to a second direct-current source 100 for a continuous re-anodizing process of the etched foil 91. Finally, the etched foil 91 is passed through a post-process tank 102 and rolled for obtaining a roll of a positive electrode foil 103. The voltage of the second direct-current source 100 is determined based on a measured voltage detected with a voltage-detecting roller 104 provided before the roll of positive electrode foil 103.

Another anodizing process is disclosed in Japanese Patent Laid-open Publication No. 2-128415. When impressed with different levels of the anodizing voltage in steps, an aluminium foil is depolarized in a certain period between any two steps of the anodizing. This will minimize a leakage current on the positive electrode foil.

Also, a manufacturing apparatus disclosed in Japanese Patent Laid-open Publication No. 58-197713 includes a pair of current electrode and voltage electrode sandwiching the electrode foil in a processing liquid. While the current electrode is fed with an alternating current, the voltage at the voltage electrode is measured by a phase sensitive voltmeter and used for controlling the anodizing process.

The conventional method of manufacturing the positive electrode foil 82 however causes the effective surface area of the etched foil 76 to vary between the etching apparatuses. This hardly ensures a constant capacitance in any capacitor with the positive electrode foil 82 manufactured from an aluminum foil 76 by the anodizing process 77 even under the predetermined anodizing conditions. That is because the dielectric oxide film is not uniform in the thickness due to a change of the current for the anodizing process 77. The change is caused by variations of the effective surface area of the foil 76.

Therefore, the step of judgment 81 is provided after the step 80 for inspecting the properties of the anodized foil 79 in the beginning of the anodizing process. When the judgment 81 is negative, the anodizing conditions are modified and re-set. This hence produces a loss in the time for manufacturing the anodized foil 79.

For continuously manufacturing the positive electrode foils 82 of different rated voltages with a single anodizing apparatus, an aluminum foil is inserted between the anodized foils 79 of different voltages for inhibiting the anodizing conditions for the preceding lot from affecting to the succeeding lot. This makes the procedure more difficult, and in worse case, produce defectives of the anodized foil 79.

Moreover, as the anodizing conditions are set by an operator, they may often have artificial errors.

The etched foil 76 is varied in the effective surface area along the lengthwise direction. This will hardly be overcome by the anodizing conditions calculated in each lot. In the conventional anodizing apparatus shown in FIG. 8, while the output of the second direct-current source 100 is controlled based on a measured voltage detected by the voltage sensor roller 104, the voltage in the tank 99 may vary corresponding to the specific resistance of the etched foil 91 between the first re-anodizing tank 99 and the voltage sensor roller 104. As a result, the positive electrode foil 103 is hardly uniform in the capacitance and the withstanding voltage along the lengthwise direction.

In the method disclosed in Japanese Patent Laid-open Publication No. 02-128415, the aluminum foils is impressed with different levels of the anodizing voltage at multiple steps, and more specifically, with a constant anodizing voltage at each tank for the anodizing process. Consequently, the withstanding voltage of the finished anodizing film can hardly be examined. As a result, a capacitor employing the positive electrode foil may hardly be uniform in the capacitance and the withstanding voltage.

In the apparatus disclosed in Japanese Patent Laid-open Publication No. 58-197713, the electrode foil is measured at a particular portion for measuring anodizing conditions using a pair of the current electrode and the voltage electrode. And thus, the anodizing condition is hardly controlled throughout the length based on the measurement at the particular position.

SUMMARY OF THE INVENTION

A method of manufacturing the positive electrode foil of an aluminum electrolytic capacitor is provided where anodizing conditions for an etched foil are optimally determined and automatically registered to minimize variations in the capacitance and the withstanding voltage along both lengthwise and widthwise directions of the positive electrode foil. And hence, it ensures the product quality and increases the production efficiency.

In the method, the current applied for developing a dielectric oxide film on the etched foil in an anodizing process is determined to be optimum for the effective surface area of the etched foil.

The method consists mainly of an etching process and an anodizing process. The etched foil produced in the etching process is subjected to a constant current inspection, and then, the anodizing conditions are calculated from the result of the constant current inspection and transferred to a control panel for an anodizing tank for setting the anodizing apparatus.

As a result, the anodizing conditions optimum for the etched foil can automatically be registered and used for the anodizing process of the foil.

Another method of manufacturing the positive electrode foil is provided where an etched foil is fed with a current from a direct-current source and conveyed between cathode electrodes provided in an anodizing tank by running rollers for the anodizing process. While the running rollers are made of metallic material, a voltage sensor is connected between one of the running rollers and the cathode electrodes. A voltage measured by the voltage sensor is fed back to the direct-current source for controlling its output voltage.

This method allows the output voltage of the direct-current source to be controlled through measuring the withstanding voltage of a dielectric oxide film developed on the etched foil in the anodizing tank. Accordingly, as the withstanding voltage of the dielectric oxide film remains constant, unwanted variations in the properties of the positive electrode foil including the capacitance and the withstanding voltage along both lengthwise and widthwise directions can be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a method of manufacturing a positive electrode foil of an aluminum electrolytic capacitor according to exemplary embodiment 1 of the present invention;

FIG. 2 is a characteristic diagram showing a resultant data of a constant current inspection in the method according to embodiment 1;

FIG. 3 is a schematic view of an anodizing tank in an apparatus for manufacturing the positive electrode foil for an aluminum electrolytic capacitor according to exemplary embodiment 2 of the present invention;

FIG. 4 is a schematic view of an apparatus for manufacturing the positive electrode foil according to embodiment 2;

FIG. 5 is a characteristic diagram of a positive electrode foil of example 4;

FIG. 6 is a characteristic diagram of a positive electrode foil of comparison 2;

FIG. 7 is a flowchart of a conventional method of manufacturing the positive electrode foil of an aluminum electrolytic capacitor; and

FIG. 8 is a schematic view of a conventional apparatus for manufacturing the positive electrode foil of an aluminum electrolytic capacitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Embodiment 1)

A method of manufacturing the positive electrode foil of an aluminum electrolytic capacitor according to Embodiment 1 of the present invention is illustrated in the flowchart of FIG. 1. In an etching process, an aluminum foil 1 from a roll having a thickness of 0.05 to 0.11 mm and a length of about 5,000 mm is continuously subjected to an etching operation 2 in an etching apparatus thus to be formed as an etched foil 4. The etching apparatus is manually preset to particular etching conditions for a desired effective surface area, through a control panel 3. The etched foil 4 in a roll is marked every 1,000 m with a lot number. Then, the etched foil 4 is subjected to a characteristic inspection 5 (conforming to EIAJ RC-2364A).

The etching operation 2, depending on the effective surface area and the production efficiency, may be carried out using an acid solution comprises 5 to 15 wt % of hydrochloric acid and 0.01 to 5 wt % of an additive such as sulfuric acid, nitric acid, phosphoric acid, or oxalic acid. The etching conditions are a temperature of 20 to 50° C., a frequency of 10 to 60 Hz, and a current density of 0.05 to 0.5 A/cm². The etching operation is repeated three to fifteen times.

This is followed by transferring data of the anodizing condition from an anodizing conditioning system to a control panel 8 in an anodizing apparatus.

The anodizing conditioning system comprises a block 12 for constant current inspection, a block 13 for analyzing and determining the anodizing conditions, and a block 14 for transferring the anodizing conditions determined, and is controlled by a computer 15.

The block 12 performs a constant current inspection on the etched foil 4 produced in the etching process. In the constant current inspection including to apply a constant current to the etched foil 4 in an electrolyte liquid, data of voltage increase and current profile such as shown in FIG. 2 is obtained.

The block 13 calculates, from the data, a quantity of electricity required for an etched foil 6 reaching at a desired voltage in the anodizing operation 7 and calculates, from the quantity, the anodizing conditions including a voltage and a current to be applied and a production speed. Before the anodizing conditions are finally determined, the current to be applied and the production speed in the anodizing operation 7 are optimized by preliminarily considering a structural arrangement of the anodizing apparatus, and the voltage to be applied is assessed.

The block 14 transfers the anodizing conditions including the voltage and current to be applied and the production speed to the control panel 8 in the anodizing apparatus where they are automatically preset.

As the anodizing apparatus has been set with the anodizing conditions, it continuously performs the anodizing operation 7 to develop a dielectric oxide film on the etched foil 6, thus producing an anodized foil 9.

The anodizing operation 7 includes immersing the etched foil 6 as a positive electrode in the solution (at a temperature of 60 to 90° C.) of ammonium adipate, phosphoric acid, or boric acid for anodizing the foil. For developing a favorable dielectric oxide film, the etched foil 6 is immersed in an ammonium adipate solution for the anodizing, depolarized, and subjected again to the anodizing operation. The anodizing operation 7 is not limited to the above-explained technique but may be carried out by any appropriate manner.

This is followed by a characteristic inspection 10 (conforming to EIAJ RC-2364A) for finishing a positive electrode 11. The resultant data of the characteristic inspection 10 may be fed back, if desired, for reviewing and modifying the anodizing conditions.

The method according to embodiment 1 allows the anodizing operation 7 to be performed with optimum anodizing conditions automatically determined for the etched foil 6. As a result, the positive electrode foil 11 of a consistent quality can be manufactured at a higher production efficiency without artificial faults.

This embodiment will be described in more detail with some examples.

EXAMPLE 1

A positive electrode foil of an aluminum electrolytic capacitor of a capacitance of 720 μF is manufactured using an anodizing voltage of 21 Vf.

An aluminum foil of 100 μm thickness from a roll of 1,000 m length is etched by an etching apparatus set with desired etching conditions to be an etched foil.

A test piece of a certain length is cut from the etched foil and subjected to a constant current inspection. In the constant current inspection, the test piece is immersed in a 15% ammonium adipate electrolyte solution and loaded with a constant current of 0.5 A/cm² to measure data of a voltage increase and a current profile.

The data is then used for calculating a quantity of electricity required for increasing the anodizing voltage up to 21 Vf. From the quantity and the structural arrangement of the anodizing apparatus used in the anodizing process, the anodizing conditions including the voltage and current to be applied and the production speed are calculated. Then, the anodizing conditions are transferred to the control panel in the anodizing apparatus where they are registered as its settings. The anodizing process is continuously performed on the etched foil by the anodizing apparatus to develop an anodized foil having a dielectric oxide film, i.e., a positive electrode foil.

EXAMPLE 2

Another set of positive electrode foils of an aluminum electrolytic capacitor of a capacitance of 720 μF is manufactured at an anodizing voltage of 21 Vf.

Three aluminum foils of 100 μm thickness from their respective rolls of 1,000 m lengths are etched by corresponding etching apparatuses which are different in the etching conditions to obtain three etched foils A, B, and C, respectively.

A test piece of a length is cut from each of the three etched foils A, B, and C and subjected to a constant current inspection. In the constant current inspection, the test piece is immersed in a 15% ammonium adipate electrolyte solution and loaded with a constant current of 0.5 A/cm² to measure the voltage increase and the current profile.

The data is then used for calculating a quantity of electricity required for increasing the anodizing voltage up to 21 Vf. From the quantity and the structural arrangement of the anodizing apparatus used in the anodizing process, the anodizing conditions including the voltage and current to be applied and the production speed are calculated for each of the etched foils A, B, and C.

Then, the anodizing conditions for the etched foil A are transferred to the control panel in the anodizing apparatus where the voltage and current to be applied and the production speed are registered as its settings. In the anodizing apparatus, the anodizing process is continuously performed on the etched foil A to develop an anodized foil A having a dielectric oxide film. The etched foil A is then joined with the etched foil B. The anodizing conditions for the etched foil B are transferred to the control panel in the anodizing apparatus where the voltage and current to be applied and the production speed are registered as its settings. As the etched foil B is subjected to the continuous anodizing operation to develop an anodized foil B having a dielectric oxide film. Similarly, the etched foil C is subjected to the anodizing operation to develop an anodized foil C. As a result, three positive electrode foils A, B, and C are completed.

EXAMPLE 3

A positive electrode foil D of an aluminum electrolytic capacitor of capacitance 1,040 μF is manufactured at an anodizing voltage of 14 Vf while another positive electrode foil E of an aluminum electrolytic capacitor of capacitance 430 μF is manufactured at an anodizing voltage of 36 Vf.

An aluminum foil of 100 μm thickness from a roll of approximately 2,000 m length is etched by an etching apparatus set with desired etching conditions, and separated into two etched foils D and E of 1,000 m length each, each being wound in a roll.

A test piece of a certain length is cut from each etched foils D and E and subjected to a constant current inspection. In the constant current inspection, the test piece is immersed in a 15% ammonium adipate electrolyte solution and loaded with a constant current of 0.5 A/cm² to measure the voltage increase and the current profile.

The data is then used for calculating two different quantities of electricity required for increasing the anodizing voltage up to 14 Vf and 36 Vf, respectively. From the quantities and the structural arrangement of the anodizing apparatus used in the anodizing process, the anodizing conditions including the voltage and current to be applied are calculated for each etched foils D and E. The production speed is identical for both the etched foils D and E.

Then, the anodizing conditions for the etched foil D are transferred to the control panel in the anodizing apparatus where the voltage and current to be applied and the production speed are registered as its settings. In the anodizing apparatus, the anodizing process is continuously performed on the etched foil D to develop an anodized foil D having a dielectric oxide film. The etched foil D is then joined with the etched foil E. The anodizing conditions for the etched foil E are transferred to the control panel in the anodizing apparatus where the voltage and current to be applied and the production speed are registered as its settings. The etched foil E is subjected to the continuous anodizing operation to develop an anodized foil E having a dielectric oxide film. As a result, positive electrode foils D and E are completed.

(Comparison 1)

A positive electrode foil of an aluminum electrolytic capacitor of a capacitance of 720 μF is manufactured for comparison at an anodizing voltage of 21 Vf.

An aluminum foil of 100 μm thickness from a roll of 1,000 m length is etched by an etching apparatus set with desired etching conditions to obtain an etched foil.

The etched foil is subjected to a continuous anodizing operation in the anodizing apparatus set with the anodizing conditions including an anodizing voltage of 21 Vf and a capacitance of 220 μF to obtain an anodized foil having a dielectric oxide film, i.e., a positive electrode foil.

For the five respective test pieces from the positive electrode foils of examples 1 to 3 and comparison 1, each capacitance and withstanding voltage are measured at positions in every 100 m length and listed in Table 1.

TABLE 1 Withstanding Capacitance Voltage Standard Standard (μF/10 cm²) Deviation (V) Deviation Example 1 Positive 715 3.3 20.6 3.4 Electrode Foil A Example 2 Positive 713 3.2 20.5 3.2 Electrode Foil B Positive 716 3.1 20.4 3.3 Electrode Foil C Positive 714 3.3 20.3 3.2 Electrode Foil D Example 3 Positive 1,043 3.4 14.3 3.3 Electrode Foil E Positive 438 3.2 36.2 3.1 Electrode Foil F Comparison 1 712 6.1 21.4 6.3

As apparent from Table 1, the positive electrode foil of example 1 is substantially equal in the capacitance and the withstanding voltage to the comparison 1 but significantly smaller in the variation than that of the comparison 1. From the measurement result of example 2, the capacitance, the withstanding voltage, and their variations of capacitors employing positive electrode foils made from three different rolls of etched foils are substantially identical to those of example 1 even if the rolls are continuously anodized.

The positive electrode foils of example 3 manufactured under different anodizing conditions continuously exhibit minimum variations in both the capacitance and the withstand voltage.

(Embodiment 2)

FIG. 3 is a schematic view of an anodizing tank used for an anodizing process of an aluminum foil. An etched aluminum foil 31 is fed with a direct-current voltage upon a direct contact with a feed roller (not shown) connected to the positive electrode of a direct-current source 37. The foil 31 is conveyed into the anodizing tank 35 by an input running roller 32 and drawn out from the anodizing tank 35 by an output running roller 33. The output running roller 33 is made of a metallic material. Cathode electrodes 34 are disposed in parallel with each other in the anodizing tank 35 filled with an anodizing solution. The aluminum foil 31 is anodized when running between the cathode electrodes 34 to have a dielectric oxide film developed thereon.

The withstanding voltage of the dielectric oxide film developed in the anodizing tank 35 is determined by a output voltage of the direct-current source 37 and may be varied depending on the effective surface area of the etched foil and the resistance of the anodizing solution. A voltage sensor 36 is connected between the output running roller 33 and the cathode electrodes 34 for measuring the withstanding voltage of the dielectric oxide film. A resultant measurement is fed back to control the output voltage of the direct-current source 37, whereby the withstand voltage of the dielectric oxide film can remain constant.

FIG. 4 is a schematic view of an apparatus for manufacturing the positive electrode foil of an aluminum foil through the anodizing process. An etched aluminum foil 41 is energized by a feed roller 42 connected to the positive electrodes of a first direct-current source 43, a second direct-current source 44, and a third direct-current source 45. An anodizing tank 46 is filled with a water solution including phosphoric acid, boric acid, or organic acid. When the cathode electrodes 49 in the anodizing tank 46 are fed with a current, a dielectric oxide film having a desired withstanding voltage is developed on the surface of the aluminum foil 41.

The anodizing tank 46 is identical in the construction to the anodizing tank 35 shown in FIG. 3. A voltage sensor 55 is connected between an output running roller 52 and the cathode electrodes 49 in the anodizing tank 46 for measuring the withstanding voltage of the oxide film. A resultant measurement is then fed back to control an output voltage of the first direct-current source 43.

A depolarization tank 58 and re-anodizing tanks 47 and 48 are filled with a water solution including phosphoric acid, boric acid, or organic acid. The re-anodizing tanks 47 and 48 are also identical in the construction to the anodizing tank 35 shown in FIG. 3. A voltage sensor 56 is connected between an output running roller 53 and cathode electrodes 50 in the re-anodizing tank 47 for measuring the withstanding voltage of the oxide film. A resultant measurement is then fed back to control an output voltage of the second direct-current source 44. Similarly, a voltage sensor 57 is provided on the re-anodizing tank 48 thus to control an output voltage of the third direct-current source 45. The foil 41 is then passed through a post-process tank 59 before rolled as a positive electrode foil 60.

The voltage sensors 55, 56, and 57 may include Wheatstone bridges so that the potential of their corresponding output running rollers 52, 53, and 54 may be equal to the potential of the aluminum foil 41. The voltage sensors 55, 56, and 57 may be arranged to provide a minimal current between the foil 41 and their corresponding output rollers 53, 53, and 54. For stable measurement of the voltage, the aluminum foil 41 and the output running rollers 52, 53, and 54 are set to a grounding potential. In particular, the method of providing a minimum current between the foil 41 and the rollers 52, 53, and 54 is most preferable for measuring the voltage easily and accurately.

On a finished positive electrode foil 60 manufactured by the above described procedure, a dielectric oxide film having a uniform withstanding voltage is formed because the output voltage of each direct-current source is controlled based on a voltage measured with the voltage sensor at the output of each anodizing tank. Consequently, variations along the lengthwise direction in the properties of the positive electrode foil including the capacitance and the withstanding voltage is declined.

The positive electrode foil manufactured by this embodiment will be described with some examples.

EXAMPLE 4

A positive electrode foil 60 is manufactured from an etched aluminum foil 41 under the anodizing conditions listed in Table 2 by the apparatus shown in FIG. 4.

TABLE 2 Anodizing Conditions Density Tempera- Voltage Process Chemical (%) ture (° C.) (V) Anodizing Boric Acid 0.1 75 22 Tank 46 Depolarization Phosphoric 0.2 60 — Tank 58 Acid Re-Anodizing Ammonium 8.0 80 22 Tank 47 Adipate Re-Anodizing Ammonium 8.0 80 22 Tank 48 Adipate Post-Process Phosphoric 1.0 60 — Tank 59 acid

EXAMPLE 5

A test piece is separated from the etched aluminum foil 41 of Example 4 and subjected to a constant current inspection. In the constant current inspection, the test piece is immersed in a 15% ammonium adipate electrolyte solution and loaded with a constant current of 0.5 A/cm² to measure the voltage increase and the current profile. They are is then used for calculating a quantity of electricity required for increasing the anodizing voltage up to 21 Vf. From the quantity and the structural arrangement of the anodizing apparatus used in the anodizing process, the anodizing conditions including the voltage and current to be applied and the production speed are calculated. The voltage and current to be applied are transferred to the first direct-current source 43 while the production speed is transferred to a control panel of the anodizing apparatus for its setting. Then, the positive electrode foils are manufactured by the same manner as of Example 4.

(Comparison 2)

The apparatus shown in FIG. 8 performs the anodizing process to an etched foil 91 under the anodizing conditions listed in Table 2. In the apparatus, a detecting roller 104 providing a voltage to control a second direct-current source 100 in order to manufacture a positive electrode foil 103.

Resultant measurements of the capacitance and the withstanding voltage of the positive electrode foils of example 4 and comparison 2 are illustrated in FIG. 5 (Example 4) and FIG. 6 (Comparison 2), respectively.

While a 10 cm²-sized test piece of the positive electrode foil is immersed in a water solution at 30° C. containing 150 g/l of ammonium adipate, its static capacitance is measured. Also, the test piece is immersed in a water solution at 70° C. containing 30 g/l of ammonium adipate and fed with a current of 0.2 mA/cm². The voltage after one minute from achievement at 90% of the desired voltage is determined as the withstanding voltage.

As apparent from FIGS. 5 and 6, the method of example 4 allows the anodizing tank and the re-anodizing tanks to be fed with a desired stable voltage, hence minimizing variations along the lengthwise direction in the capacitance and the withstanding voltage of the positive electrode.

Table 3 shows standard deviations of the capacitance and the withstanding voltage of the positive electrodes of examples 4 and 5 and comparison 2.

TABLE 3 Standard Deviation Withstanding Capacitance Voltage Example 4 0.286 0.085 Example 5 0.235 0.056 Comparison 2 2.31 0.387

As apparent from Table 3, the positive electrode foils of Examples 4 and 5 have less variations and are stable in the properties.

The apparatus according to embodiment 2 allows the aluminum foil 41 to run forward and backward in the three anodizing tanks fed with a desired voltage, but is not limited to that. Even if the number of the tanks and the number of the forward and backward movement increases as desired, the output voltage of each source is controlled with the corresponding voltage sensor, and thus, variations on the positive electrode foil are minimized.

Further, the present invention is not limited to the aluminum foil 41 fed with a current at one location. For example, the current may be fed through each anodizing tank.

The higher the production speed or the lower the desired voltage, the greater a change in the voltage due to the resistance of the aluminum foil 41 becomes. Accordingly, the effect of controlling the output voltage of each source with the voltage sensor is emphasized.

The manufacturing method according to embodiment 2 may be combined with that according to embodiment 1. 

What is claimed is:
 1. A method of manufacturing a positive electrode foil of an aluminum electrolytic capacitor using a manufacturing apparatus having an anodizing apparatus for anodizing an etched foil, comprising: performing a constant current inspection of an etched foil to calculate a quantity of electricity for the etched foil to reach a predetermined voltage; calculating an anodizing condition from the calculated quantity of electricity; transferring the anodizing condition to the anodizing apparatus for setting the anodizing apparatus; and subjecting the etched foil to an anodizing process of the anodizing apparatus.
 2. The method according to claim 1, wherein said performing the constant current inspection comprises: applying a constant current to the etched foil; and measuring a voltage and a current on the etched foil.
 3. The method according to claim 1, wherein said calculating the anodizing conditions comprises calculating a voltage and a current to be applied to the etched foil and a production speed in the anodizing apparatus.
 4. A method of manufacturing a positive electrode foil of an aluminum electrolytic capacitor using a manufacturing apparatus having an anodizing apparatus including an anodizing tank having a plurality of cathode electrodes, the method comprising: performing a constant current inspection of an etched foil to calculate a quantity of electricity for the etched foil to reach a predetermined voltage; calculating an anodizing condition from the calculated quantity of electricity; transferring the anodizing condition to the anodizing apparatus for setting the anodizing apparatus; applying a first direct-current voltage to the etched foil; conveying the etched foil between the cathode electrodes; measuring a second voltage between the etched foil and the cathode electrodes; and controlling the first voltage according to the second voltage.
 5. The method according to claim 4, wherein said performing the constant current inspection comprises: applying a constant current to the etched foil; and measuring a voltage and a current on the etched foil.
 6. The method according to claim 4, wherein said calculating the anodizing condition comprises calculating a voltage and a current to be applied to the etched foil and a production speed in the anodizing apparatus.
 7. The method according to claim 4, wherein said measuring the second voltage comprises applying a constant current to the etched foil.
 8. A method of manufacturing a positive electrode foil of an aluminum electrolytic capacitor using a manufacturing apparatus having an anodizing apparatus for anodizing an etched foil, comprising: performing a constant current inspection of the etched foil; calculating an anodizing condition from a result of the constant current inspection, the anodizing condition including a voltage and a current to be applied to the etched foil and a production speed in the anodizing apparatus; transferring the anodizing condition to the anodizing apparatus for setting the anodizing apparatus; and subjecting the etched foil to an anodizing process of the anodizing apparatus.
 9. The method according to claim 8, wherein said performing the constant current inspection comprises: applying a constant current to the etched foil, and measuring a voltage and a current on the etched foil.
 10. A method of manufacturing a positive electrode foil of an aluminum electrolytic capacitor using a manufacturing apparatus having an anodizing apparatus including an anodizing tank having a plurality of cathode electrodes comprising: performing a constant current inspection of the etched foil; calculating an anodizing condition from a result of the constant current inspection, the anodizing condition including a voltage and a current to be applied to the etched foil and a production speed in the anodizing apparatus; transferring the anodizing condition to the anodizing apparatus for setting the anodizing apparatus; applying a first direct-current voltage to the etched foil; conveying the etched foil between the cathode electrodes; measuring a second voltage between the etched foil and the cathode electrodes; and controlling the first voltage according to the second voltage.
 11. The method according to claim 10, wherein said performing the constant current inspection comprises: applying a constant current to the etched foil; and measuring a voltage and a current on the etched foil. 